A roller door is usually constructed to have a curtain which is guided by tracks, and descends as the door closes, and ascends as the door opens. In some instances the movement of the curtain is effected by power means, for example a reversible electric motor coupled to rotate the roller on which the curtain rolls. To improve stiffness, flexibility and appearance, the profile of the curtain usually includes a plurality of deformed ribs extending transversely across it.
An accident hazard exists for example with small children in that inadvertent operation of the motor causing the door to descend can make it possible for the whole weight of the curtain to bear down upon a small child, animal or the like, and it is the main object of this invention to provide means which will sense obstruction to downward movement (otherwise than at the termination of the closing action), and having sensed that obstruction, will reverse the motor driving the roller so as to lift the curtain clear thereof. Such an arrangement is required to be effective in greatly reducing accident hazards, particularly to children.
This problem has been recognised previously, and the reader may refer to U.S. Pat. No. 4,342,354 (Levenzon), constituting the closest prior art known to the Applicant herein. However, that patent was directed to a mechanism wherein the motor was carried on a swinging arm and moved in a direction out of gear mesh upon excessive loading being applied. A further object of this invention is to provide a more sensitive device than that disclosed in U.S. Pat. No. 4,342,454.